Method of forming fragrance releasing pull-apart sheets

ABSTRACT

Fragrance releasing pull-apart sheets may be more consistently and easily manufactured by coating opposed surfaces with a binder, placing microcapsules between the two surfaces with binder, and adhering the surfaces together with the binder and/or additional binder applied with the capsules.

This is a continuation of application Ser. No. 07/211,870 filed June 27,1988, now abandoned.

FIELD OF THE INVENTION

This invention relates to microencapsulated materials, articlescontaining microencapsulated materials and the method of preparing sucharticles In particular, the present invention relates tomicroencapsulated materials adhesively secured between two temporarilyadhered coated paper surfaces such that upon separation of said twosurfaces, the capsules rupture, releasing material contained therein.

BACKGROUND OF THE INVENTION

Encapsulated materials have been used for many years in a wide varietyof commercial applications. Early uses of encapsulated materialsincluded paper coated with capsules bearing coloring material thereinwhich could be used as a recording medium. U.S. Pat. No. 3,016,308discloses one of the early efforts using encapsulated material as theimage source on recording paper. U.S. Pat. Nos. 4,058,434 and 4,201,404show other methods of application of encapsulated coloring materials onpaper substrates to be used as imaging media and the like. U.S. Pat. No.3,503,783 shows microcapsules having coloring material therein which arerupturable by the application of heat, pressure and/or radiation becauseof a metal coating on the surface of the capsule. These rupturablemicrocapsules, in one embodiment, may be secured between a substrate anda photoconductive top coat to enable photosensitive imaging of thesystem.

A wide variety of processes exist by which microcapsules can bemanufactured. These varied processes provide different techniques forproducing capsules of varying sizes, alternative materials for thecomposition of the capsule shell and various different functionalmaterials within the shell. Some of these various processes are shown inU.S. Pat. Nos. 3,516,846; 3,516,941; 3,778,383; 4,087,376; 4,089,802;4,100,103 and 4,251,386 and British Patent specification Nos. 1,156,725;2,041,319 and 2,048,206. A wide variety of different materials may alsobe used in making the capsule shells. A popular material for shellformation is the polymerization reaction product between urea andformaldehyde or melamine and formaldehyde, or the polycondensationproducts of monomeric or low molecular weight polymers of dimethylolureaor methylolated urea with aldehydes. A variety of capsule formingmaterials are disclosed, for example, in U.S. Pat. Nos. 3,516,846 and4,087,376 and U.K. Patent Specification Nos. 2,006,709 and 2,062,570.

As shown in these references, the principal utility of microencapsulatedmaterials is in the formation of a surface coated with the microcapsulesin a binder. The microcapsules are ruptured by various means to releasethe material contained therein. In addition to release of physicallyobservable materials such as ink in order to form a visible image, othertypes of active ingredients such as odor releasing materials,bacteriostatic materials, chemically active materials and the like havebeen provided in this manner.

U.S Pat. No. 4,186,743 describes the use of microcapsules on a pressuresensitive adhesive between two surfaces on a sanitary napkin. When acover layer is removed, capsules are broken and the fragrance isreleased.

U.S. Pat. No. 4,487,801 describes the use of a non-pressure sensitiveadhesive layer between two surfaces, the layer having fragrancecontaining microcapsules therein. Upon separation of the two surfaces,the adhesive and the microcapsules are ruptured, releasing thefragrance. U.S. Pat. No. 4,720,417 shows a similar article in which thetwo surfaces are coated paper surfaces.

With the wide variety of paper stocks being used in the printingindustry, different formulations of adhesive must be made and optimizedto obtain the desired bonding and rupture strengths in these fragrancesampling articles.

SUMMARY OF THE INVENTION

A liquid releasing device may be manufactured as follows: Two opposedsurfaces are first coated with a first solvent activatable binder layer.A second coating composition comprising a liquid containingmicrocapsules in a liquid carrying medium is applied between the twocoated surfaces and the surfaces are bonded, by the second coatingcomposition or the action of the liquid carrying medium is a solvent,upon drying. The solvent in the coating composition may activate thefirst binder without dissolving the microcapsules. The mechanicalproperties of the adhered composite (the rupture force and bindingstrengths) can be adjusted simply by changing the weight per unit areaof the first binder.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an article comprising at least twosurfaces, sheets or opposed faces of a folded single sheet temporarilysecured by means of a base coating on each of the opposing faces of thesheets and a third adhesive layer having microcapsules dispersedtherein. Generally flexible sheets of paper are preferred. Coated paperis preferred and is a conventional and standard item in commerce. It isgenerally a fibrous sheet having a pigment-bearing resinous coating onone or both surfaces. Usually the pigment provides a white, bone orivory coloration to the sheet. Most generally pigments producing a whitecoloration are used. The binder used in the resinous coating isgenerally colorless and/or transparent. The binder is generally asynthetic or natural organic polymeric material. Typical pigments forproducing white coated paper are fine white pigment such as clay,calcium carbonate, titania, silica, zinc oxide, etc. Typical bindersinclude latices (e.g., styrene-butadiene, butadiene-acrylonitrile,etc.), film-forming polymers (e.g., polymethylmethacrylate), and naturalresins (e.g., casein, ammonium caseinate, starch, etc.). The coatingsusually comprise between 65-90% by weight of pigment, preferably 70-80%by weight of pigment, and 10-35% by weight of binder, preferably 20-30%by weight of binder. Papers having both sides coated are preferred inthe advertising trade.

The properties of such paper coatings as are commonly encountered incommerce vary widely from one manufacturer to another and even from lotto lot. This has made it necessary to adjust the composition, coatingweight, and coating conditions for each individual production run inorder to obtain the best balance of peel force and capsule rupture inthe products of the prior art. We have found that a base coating appliedto the paper stock prior to the application of the capsule containinglayer may greater reduce the variability previously encountered. Thebase coatings are believed to function, in part, by controlling the rateand degree to which the carrier liquid for the capsule containing layerpenetrates the underlying paper. This in turn influences the effectiveamount and distribution of binder in the dried capsule containing layerand the resulting mechanical properties of the layer. We have furtherfound that it is preferably desirable to select the polymer employed toform the base coat layers from materials which will act as an adhesivefor the capsules when wet by the carrier liquid used to apply thecapsule containing layer.

In the event that the polymer of the base coat layers is not soluble inor softened by the carrier liquid for capsules, it is desirable toinclude a separate binder in the capsule containing layer. This binderis usually employed at lower levels than those of the prior art capsulecoating systems.

The adhesive material for the capsules must form a bond to the coatedsurfaces of the sheets which is stronger than the cohesive strength ofthe adhesive with the capsules dispersed therein. Although it isgenerally desirable to have an adhesive, the absolute cohesive strengthof which is less than its adhesive strength to the coated surface of thecoated paper cover sheets, this is not essential. When capsules areincluded within the adhesive composition, the effective cohesivestrength of the adhesive tends to be reduced. Adhesives, which bythemselves would cause the sheets to be damaged during separation, canbe used in combination with capsules in the practice of the presentinvention because of lowered effective cohesive strength. The capsulesin the present invention may comprise any rupturable capsule containingan active ingredient therein. The active ingredient may be a fragrance,medicinal liquid, one part of a two part reactive system, testindicator, repellent, or the like The tensile rupture strength of thecapsules must be such that the cohesive failure of the adhesive resultsin capsule breakage. It has also been found that the size of thecapsules plays a role in the usefulness of capsules within rupturablesheets according to the practice of the present invention. Generally thecapsules should have an average diameter between 6 and 500 microns andpreferably between 12 and 30 microns when the capsule payload is between80 and 90% by weight of the total capsule weight. It is highly preferredthat the capsules have an average diameter between 14 and 26 microns andit is most preferred that the capsules have a diameter between 15 and 25microns. These dimensions play a surprisingly important role in theability to control the percentage of rupture of capsules in the practiceof the present invention. With lower payloads (e.g., 70-80%), thecapsules should be larger to provide the necessary rupture strength. Thebroadest range of average capsule size under most conditions would beabout 4 to 80 microns. When 8 micron capsules are used, a 90-95% byweight payload is preferred. Eight to thirty micron capsules aregenerally preferred

The capsules should form between 20 and 99 percent by volume of thetotal adhesive composition, and preferably between 90 and 98 percent ofthe total composition volume. If certain microcapsule shell materialsare used, such as gelatin, the capsule may comprise as much 100% of theadhesive compositions. The absolute peel force tends to be dependent onthe weight the base coat and relatively independent of the amount ofcapsules (up to 50% by weight capsules).

As previously noted, the prior art compositions have to be formulatedfor differing substrates. This can be a time consuming and expensiveeffort, particularly for small sampling orders. By practicing theteachings of the present invention, single compositions or pairs ofcompositions can be used to adhere substantially all polymeric or papersurfaces including uncoated paper stocks. Any commercial base stock maybe used.

The essential characteristics and features of the present inventioninclude a process for adhering two surfaces together with a microcapsulefilled binder, the process comprising the steps of

(a) coating two surfaces with an adhesive which may or may not be asolvent activatable first adhesive,

(b) applying a coating composition between said two surfaces, saidadhesive composition comprising a liquid carrying medium andmicrocapsules containing a liquid fill therein (and optionally a secondadhesive),

(c) and bringing said surfaces into adhesive contact with each other tobind them together

The two opposed surfaces may be the same or different. There may be afirst adhesive in said base coating composition and a said secondadhesive may be present in the capsule composition, said second adhesivealso may be the same or different material from said first adhesive.Both adhesives may be swellable, softenable, or soluble the solvent ofthe adhesive composition. The solvent or carrier liquid also must notquickly dissolve the microcapsules (e.g., in less than one hour). Thefirst adhesive dries to some extent before the capsule coatingcomposition is applied and may be intentionally air dried or oven driedbefore the adhesive composition is applied.

The solvent may be water or organic solvents or mixtures thereof. Theorganic solvents may be polar or non-polar, depending upon the solvationrequirements of the binders.

The bonding of the surfaces may be effected in a number of alternativefashions. The base coatings on both opposed faces of the sheets may bethe sole adhesive coating compositions. This can be done by applying themicrocapsule slurry composition between the opposed faces either (1)before complete drying of the base coat so that it can act as anadhesive without further solvent activation (some thermal activation maybe desirable), or (2) after drying but with the microcapsule slurrycoating composition containing a liquid carrier medium which is anactivating solvent for the adhesive in the base coat, or (3) afterdrying but with the microcapsule slurry coating composition containingsufficient amounts of an adhesive which can bond the two adhesive(polymer) coated opposed faces together. The binder or adhesive shouldnot be a pressure-sensitive adhesive as these perform extremelyinefficiently and poorly.

The areas of bonding between the opposed faces can be made discontinuousin a very easy procedural modification. By printing the base coatadhesive composition in a discontinuous manner and not using anysignificant amount of adhesive (e.g., a polymeric thickener may be usedto increase the viscosity of the microcapsule slurry) in themicrocapsule slurry coating composition, the opposed faces will beadhered only in those areas where the base coat adhesive has beenprinted. The slurry carrying medium is usually a solvent for the basecoat adhesive in this embodiment. The microcapsules will lightly adhereto the faces of the sheet, but will not rupture upon separation of theopposed faces. This will allow for reuse of the fragrance; i.e.,additional microcapsules can be ruptured by scratching after the sheetshave been separated.

The binders may be water-soluble, aqueous-swellable, or organic solventsoluble. Preferred binders' are at least water-softenable binders suchas polyvinyl pyrrolidone, gelatin, polyvinyl alcohol, hydroxyethylcellulose, hydroxypropyl cellulose, or may be organic solvent solublepolymers such as polyvinyl ethers, polyacrylates, polyamides, polyester,polyvinyl chloride, polyvinylidene chloride, polylyrene, and mixtures,blends, or copolymers of these types of materials.

It is particularly desirable in the present invention to use an amountof binder in the capsule layer coating composition which is too small toform an adhesive bridge between the two surfaces by itself. This wouldrequire the use of binders which are present at less than 10% by weightof the capsule weight, preferably less than 7% and most preferably lessthan 5% and greater than 0.2%. Larger concentration of binder (e.g.,80%) can be used, but the preferred practice is as just described.

The present invention enables the manufacture of a device for exposing aliquid (e.g., to the atmosphere, said device comprising:

(1) at least two surfaces of coated or uncoated paper bound by anadhesive composition base coat layer,

(2) a composition layer between said base or film coat layers on saidsurfaces containing microcapsules with said liquid within the shell ofsaid microcapsules, and

(3) said microcapsules having an average diameter between 4 and 500micrometers, the cohesive strength of the adhesive composition layerbeing less than the strength of the bond between said adhesivecomposition and a coated face of said sheets, the tensile rupturestrength of said microcapsules being less than the cohesive strength ofthe adhesive composition, and the rupture force of said microcapsulecontaining adhesive composition layer at 50% relative humidity beingbetween at least 2 ounces per linear five-and-one-half inches and lessthan 45 ounces per linear five-and-one-half inches (greater than 4.0g/cm and less than 90 g/cm). It is preferred that the rupture strengthbetween the sheets exceeds 8.0 g/cm and is less than 80 g/cm and mostpreferably exceeds 16 g/cm and is less than 75 g/cm. The minimumstrength at this ambient condition (i.e., 23° C. and 50% R.H.) isnecessary to keep the sheets from falling apart from forces incurredduring handling. This problem has frequently occurred in magazineinserts where coated paper has been used. The maximum limit on therupture strength is necessary to keep the paper from tearing (termedfiber pull or fiber rupture) before the adhesive and capsules rupture.This would prevent release of the liquid from the capsules.

It is also desirable to have the construction resist the effects ofvariable ambient conditions. Certain products presently used on uncoatedpaper stock work in ambient conditions but fail in transit or on storageas the temperature and humidity change. Given the fact that some ofthese compositions fail at even standard conditions (23° C. and 50%R.H.), they tend to fail worse at more extreme conditions such as 26.5°C. and 80% R.H. or on dry conditions. For example, some binders orcapsules are dehydrated by storage in heated warehouses during thewinter and become so fragile that simple handling will rupture them.Complaints have been made by purchasers of magazines that all of thevarious odors in inserts are being released prior to usage of themagazine. The entire magazine tends to have a strong composite odor ofmany scents rather than being able to provide distinct samples ofindividual scents. It is therefore desirable that rupture strengthexceed 4.0 g/cm after storage at 49° C. and less than 10% R.H. forseventy-two hours. This test may be performed by storage in an oven,removal to a neutral environment (e.g., sealed bag or jar) until thearticle is at room temperature, and then measuring the rupture strength.It is preferred that the rupture strength is at least 4 to 8.0 g/cm andmost preferred that the rupture strength is at least 16 g/cm under thoseconditions. The article must still display a rupture strength between 4and 90 g/cm at 23° C. and 50% R.H.

A number of methods have been found which enable these conditions to bemet according to the present invention. The use of viscosity increasingagents in the capsule containing coating composition provides a moreeven coating and one that ruptures before fiber pull begins. The use ofadditional coatings over the coated paper which contain polymersdifferent from the binder of the adhesive layer and which do not form asolution or chemically bond to the binder of the adhesive layer providesa useful article according to the present invention. The use of largersize capsules tends to weaken the cohesive strength of the adhesivecomposite and prevent fiber pull. The use of capsules which are notmoisture sensitive in combination with these large capsules (i.e.,greater than 30 microns and up to 500 microns) provides a usefuladhesive layer. Higher capsule-to-binder ratios reduce the cohesivestrength of the adhesive, as may the addition of non-viscosity enhancingparticulate fillers. The viscosity increasing agents described in U.S.Pat. No. 4,720,417 been found to be useful in the coatings of thisinvention.

The inorganic particles tend to be preferred. The viscofier enhancershave been found to be necessary in dry weight proportions of theadhesive mix in amounts of from 0.25 to 12% by weight, preferably from 5to 12% by weight. In general, the weight proportions of materials in thedried adhesive layer according to the present invention are generally asfollows:

    ______________________________________                                        Microcapsules     80%-100%                                                    Adhesive         20%-0%                                                       Viscosity Enhancers                                                                              0.0-10%                                                    ______________________________________                                    

The slurry composition may vary from 98% capsules and 2% liquid mediumto 10% capsules and 90% liquid medium with 0-50% binder present.

The ability to use coated paper in the manufacture of these articles isimportant because that material is the standard printing medium of thetrade. Those papers enable the highest quality printings to be made incombination with the releasable materials of the present invention.

The nature and composition of the adhesive binder is not critical to thepractice of the invention as long as the required functional, adhesiveand cohesive properties are met. The adhesive may be pressure sensitive,water or solvent borne or thermally activatable. A single layer of anon-pressure-sensitive adhesive is preferred. There is no need forrejoining the sheets after rupturing of the capsules and so the pressuresensitive function is not necessary.

The base coat layer and the adhesive (with microcapsules) may be appliedbetween two separate sheets in either a continuous or discontinuouspatterns. It is usually desirable to leave at least some portion of atleast one outer edge of the sheets unbonded so as to provide an areawhere separation can be easily started. A single sheet may be folded soas to form two facing sheets joined along one edge. The adhesive may beapplied on the interior area adjacent to the fold. This provides afolded article that can be readily opened, rupturing the capsules, yetleaves a single artifact rather than two sheets after use.

It is preferred that the capsule-bearing adhesive coated inside portionof the single sheets (e.g., from the fold to the end of the adhesive)constitute from 5 to 40% of the surface area of the sheets. In two sheetconstructions, 10 to 95 percent adhesive coverage is used. Some uses mayallow for only a single corner to be uncoated so as to provide astarting point for the separation of the sheets, but the 5 to 40% rangeis preferred with 10 to 30% more preferred in two sheet constructions.

Any class of adhesives including but not limited to polyurethanes,polyacrylates, polyvinyl resins (e.g., polyvinyl alcohol, polyvinylchloride), polyamides, polyesters, polyolefins, starches, gum arabic,gelatin and the like may be readily used in the practice of the presentinvention. These materials may be applied from either water or organicsolvents depending on the solubility of the individual materials.Washing of the capsules before coating them over the base coat adhesivetends to provide more consistency in their properties by removing lowmolecular weight, unreacted materials.

In effect, to best practice the present invention it is desirable thatcertain properties within the article have relative values for each ofthe materials used. The cohesive strength of the sheet material shouldexceed the adhesive strength between the base coat binder and the sheet.The adhesive strength of the base coat binder to the sheet should exceedthe cohesive strength of the binder. The cohesive strength of the basecoat layer and any binder present in the capsule layer should exceed thetensile rupture limits of the capsules.

As previously noted, the size of the capsules has an important effectupon the practice of the present invention. With capsules less than 8microns, there tends to be less rupturing of the capsules as to preventthe useful and efficient release of materials. Above 50 microns, theparticles are so large that additional care is necessary in handling ofthe sheets and manufacturing procedures. Furthermore, with the largesize particles it is extremely difficult to control bursting uponseparation of the sheets because of increased effects upon adhesive andcohesive properties of materials in contact with the capsules. Thepreferred ranges of 8 to 30 and 15 to 25 microns is important to thepractice of the present invention. Within these limits, rupture inexcess of 50 percent of the capsules can be easily obtained. Rupture inexcess of 80 percent of the capsules can often be accomplished in thepractice of the present invention within those limits.

The capsules may contain a wide variety of active materials therein. Theleast useful of materials to be included therein would be coloringagents since separation of the sheets would generally produce uniformcoloration rather than a distinct image. The most preferred types ofingredients would be fragrant materials (such as essences and perfumes)or materials which provide chemically active vapors or liquids (e.g.,bacteriostats or deodorants) to be wiped on or transferred to anothersurface. These may or may not also be colored. For example, a testingkit for presence of chemical vapors could be produced by providingmaterial within the capsules which would react with the vapor phasematerial for which a leak is being investigated. By separating thesheet, rupturing the capsules and exposing the vapor test material, acolor forming reaction in the air or on the sheet could be readilyobservable. Another particularly useful format would be to include themicrocapsules within a water-remoistenable adhesive and to use themixture as the binding adhesive for novelty envelopes. For example, themicrocapsules could contain the aromatic essence of baby oil, cake orpizza for invitation envelopes for a baby shower, wedding (or birthdayparty), or general party, respectively. The sides of the sheets with thecapsule-bearing adhesive thereon are preferably printed under theadhesive or adjacent the adhesive.

This invention may be practiced with a number of various modificationsthat provide new and useful articles and processes. For example, theadhesive composition with capsules may be associated with variousprinted formats to form novelty items. The exterior sheets or exposedinner face of the sheets may have questions or stories or rhymes, andunder the adhesive may be a printed picture answering the question,depicting the story or completing the rhyme, with the released fragranceemphasizing the picture further.

The capsule bearing adhesive layer in the construction of the presentinvention may also be used for a security device. In an article such asa coupon, lottery ticket or gaming card, the important display could belocated under the adhesive. Once the article had been opened and thefragrance released, any subsequent recipient would be aware of its prioruse and could be apprised of the possibility of tampering. The adhesivebeing non-pressure sensitive, it is not repositionable, the sheets arenot easily rebonded, and there would be no release of fragrance if thesheets were rebonded with additional non-fragranced adhesive andreopened. The absence or reduced level of fragrance would indicate thatthe article had been tampered with.

These and other aspects of the present invention will be shown in thefollowing examples.

EXAMPLE I

An oil having the aroma of roses was encapsulated in a urea-formaldehyderesin made according to the process of Example 20 of U.S. Pat. No.3,516,941. The capsules had an average diameter of about 17 micrometersand an estimated payload of 85% by weight (ratio of oil to total capsuleweight).

The following coating formulations were then prepared.

    ______________________________________                                        Base Coat                                                                     10% by weight hydroxypropyl cellulose in                                      ethanol                                                                       Fragrance Coat                                                                98% Capsules                                                                  2% hydroxypropyl cellulose                                                    ______________________________________                                    

A web off-set printing press with two ovens was used to manufacture thesamples. Coated paper stock was printed then dried in the first oven.The base coat was then applied in a stripe over an unprinted area invarious amounts and dried in the second oven. The fragrance coat wasthen applied in various amounts over the dried base coat, the paperfolded along the stripe and air dried for twenty-four hours. The dataare as follows:

    ______________________________________                                                 Base Coatings  Fragrance Coating                                     Sample   Weight (lbs/1300 ft.sup.2)                                                                   (lbs/1300 ft.sup.2)                                   ______________________________________                                        1        0.500          2.50                                                  2        0.625          2.50                                                  3        0.625          3.00                                                  4        0.625          3.50                                                  ______________________________________                                    

The mechanical strength was greater in samples 2-4 than sample 1(because of the greater base coat weight) and the fragrance strengthwas, as expected the greatest in sample 4.

It was found that fragrance delivery is improved by this process sincethe fracture of the material between the two surfaces occurs primarilyin the fragrance coat and not in the base coat.

By making the base coat discontinuous (e.g., leaving the end areas alonga fold uncoated) and using the preferred low amounts of binder in thefragrance layer, an area of unruptured capsules will be left on the areauncoated by the base coat layer if the fragrance coat is laid down as acontinuous stripe along the fold. This enables an initial release offragrance upon separation of the surface and a repeat release uponscratching the areas containing intact capsules.

We claim:
 1. A method of manufacturing liquid releasing devicescomprising the steps of:(1) providing two opposed surfaces, (2) coatingeach of said two opposed surfaces with a binder, (3) applying acomposition between said opposed surfaces with a binder, saidcomposition consisting essentially of microcapsules having a liquid filltherein and a liquid carrying medium free of adhesive, and (4) bondingsaid surfaces together and trapping said microcapsules therebetween withsaid binder.
 2. The method of claim 1 wherein said liquid carryingmedium is a solvent for said binder.
 3. The method of claim 1 whereinsaid two opposed surfaces comprise coated paper surfaces.
 4. The methodof claim 2 wherein said two opposed surfaces comprise coated papersurfaces.